This invention relates generally to oxygen delivery systems, and more particularly to a system which includes an oxygen conserver which operates pneumatically to provide oxygen on demand (i.e., upon inhalation).
Oxygen delivery systems of the type used by ambulatory persons, for example, typically include a source of oxygen (e.g., an oxygen bottle) for holding a supply of oxygen at pressures of up to about 3000 psi, a regulator system for reducing the pressure of the oxygen to a pressure suitable for breathing, and a cannula for delivering oxygen to the person. To increase the life of the oxygen supply, oxygen conservers are frequently used. These devices interrupt the flow of oxygen to the person using the system, either in response to exhalation, or at timed intervals, thereby reducing the rate of oxygen consumption.
Conservers are generally of two types, those which operate electrically and those which operate pneumatically. Electronic conservers require a power source (e.g., batteries) for operation, thus necessitating periodic replacement or recharging of the power source. The remaining life of the power source, which users of the system must take into consideration, can be uncertain. Pneumatic conservers, on the other hand, are operated by the inhalation and exhalation of the person using the system. They require no power source and thus have a significant advantage over electrical conservers. However, unlike electronic conservers which typically use a standard single-tube cannula, conventional pneumatic conservers generally require a double-tube cannula, one tube for supplying oxygen to the person wearing the cannula, and the other for connection to a sensing port on the conserver. The pneumatic conserver responds to changes in pressure in the sensing tube to provide oxygen to the person during inhalation, and to interrupt the flow of oxygen to the person during exhalation (when oxygen is not needed). Due to their lesser availability, expense, weight and bulk, double-tube cannulas are not popular. As a result, the use of pneumatic conservers is not widespread, despite their inherent advantages over electrical conservers. Moreover, conventional pneumatic conservers are relatively complex in design, requiring a series of spring-activated diaphragms and the like.
Some prior oxygen conservers are selectively operable in two modes. In the first (oxygen conserving) mode, oxygen is supplied to the user of the system on an interrupted basis, as described above. In the second (continuous flow) mode, a continuous stream of oxygen is provided to the user during both inhalation and exhalation. (Continuous delivery during the entire breathing cycle is not necessary for health reasons, but some persons prefer this.) These conservers are sometimes equipped with a flow control mechanism which can be adjusted to vary the rate at which oxygen is delivered. However, in prior systems, this mechanism has been operable only in the oxygen conserving mode, not in the continuous mode. Another disadvantage of certain prior oxygen delivery systems is that they are rather bulky, which makes such systems more obtrusive and reduces mobility.
There is a need, therefore, for a pneumatic oxygen conserver which can be used as part of a delivery system which overcomes the disadvantages of prior systems.